Tin plating electrolyte compositions

ABSTRACT

There is a disclosed composition suitable for use in a process for electroplating surfaces with tin, comprising: a) one or more acids selected from sulphuric acid, sulphamic acid, aryl sulphonic acids, alkyl sulphonic acids and alkanol sulphonic acids, b) one or more addition agents comprising a mono-, di- or tri-substituted phenol (each optionally alkyoxylated) or a mixture of two or more such compounds, in which at least one of the substituents includes a secondary, tertiary or quaternary nitrogen atom, c) a tin source and d) water. There is also disclosed a method of tin plating using the composition of this invention.

This invention relates to electrolyte compositions suitable forelectroplating surfaces with tin, e.g., in high speed strip or wireplating processes.

Ideally an electrolyte should possesses the following properties:produce a wide plating range, give a good quality deposit, have lowcorrosivity, have good conductivity, have good antioxidant properties,have low toxicity and have low environmental impact.

Many electrolyte compositions have been made known and are available inthe art. Typical baths include aqueous acidic baths based uponfluoroborate and fluorosilicate electrolytes as described, for example,in U.S. Pat. No. 3,769,182 and U.S. Pat. No. 4,118,289. Aryl sulphonicacids have been used in electroplating baths as disclosed, for example,in U.S. Pat. No. 3,905,878. Traditionally, the aryl sulphonic acid ofchoice is phenolsulphonic acid as used in the Ferrostan process.

Mineral acid (especially sulphuric acid) electroplating baths have alsobeen described. For example, U.S. Pat. No. 2,156,427 describes a bathcontaining tar acids and sulphuric acid for producing tin coatings of afine crystalline texture.

Alkane sulphonic acids containing 1 to 5 carbon atoms in the alkyl grouphave previously been used in certain electrolytic plating baths and werefirst disclosed for this use in U.S. Pat. No. 2,522,942. More recently,methanesulphonic acid has been claimed as a specific preferred exampleof an alkane sulphonic acid in combination with a number of brighteningagents for use in the electroplating of tin, lead and tin-lead alloysfor example as in U.S. Pat. No. 4,565,610 and U.S. Pat. No. 4,617,097.Systems based on methanesulphonic acid however suffer from high cost,toxicity, odour problems and have been known to introduce surfacedefects on flow brightened strip steel plate.

Various plating bath compositions comprising an alkane or alkanolsulphonic acid (normally methane sulphonic acid), a tin and/or a leadsalt and various auxiliary additives are known. Known auxiliaryadditives range from smaller organic molecules to large polymericsurfactant molecules and are described in U.S. Pat. No. 4,555,314, U.S.Pat. No. 4,565,609, U.S. Pat. No. 4,582,576, U.S. Pat. No. 4,599,149,U.S. Pat. No. 4,617,097, U.S. Pat. No. 4,666,999, U.S. Pat. No.4,673,470, U.S. Pat. No. 4,701,244, U.S. Pat. No. 4,828,657 and U.S.Pat. No. 4,849,059.

Plating bath compositions containing mixtures of aryl and alkylsulphonic acids are also known in the art, for example, as described inEP 0 490 575.

Various addition agents have been proposed which enhance the quality ofthe tin plate. They can include condensates of hydrophobic organiccompounds with alkylene oxides such as, for example, alpha naphthol 6mol ethoxylate (‘ENSA 6’ as supplied by Emery-Trylon); alkylbenzenealkoxylates such as the ‘Tritons’; derivatives of N-heterocycles suchas, for example, 2-alkylimidazolines; aromatic aldehydes such asnaphthaldehyde; derivatives of 2,2-bis(4-hydroxyphenyl)propane, forexample, as ‘Diphone V’ (supplied by Yorkshire Chemicals) formed byreacting 2,2-bis(4-hydroxyphenyl) propane with a sulphonating agent; and2,4,6-substituted phenols in which at least one of the substituentsincludes a secondary, tertiary or quaternary nitrogen atom as describedin U.S. Pat. No. 3,954,573. The latter addition agents have, howeveronly been described for use in fluoroborate tin plating systems.

In the case of strip tinplate manufacture it is desirable from acommercial point of view to have a system capable of giving satisfactorytin deposits over as wide as possible a range of current densities toaccommodate all variations in speed of production and minimise theincidence of current density defects.

Accordingly this invention provides a composition suitable for use in aprocess for electroplating surfaces with tin, which exhibits all theaforementioned benefits of wide plating range, good quality deposits andenhanced environmental benefits.

It comprises:

a) One or more acids selected from sulphuric acid, sulphamic acid, arylsulphonic acids, alkyl sulphonic acids and alkanol sulphonic acids.

b) One or more addition agents comprising a mono-, di- ortri-substituted phenol (each optionally alkyoxylated) or a mixture oftwo or more such compounds, in which at least one of the substituentsincludes a secondary, tertiary or quaternary nitrogen atom. The phenolis preferably a 2,4 or 2,6-disubstituted or 2,4,6-trisubstituted phenol.

c) A tin source.

d) An antioxidant (optional).

e) Water.

Preferably tin source is a tin salt. Alternatively the tin source may beelemental tin.

The acid may be any single acid or combination of acids. Preferredexamples of acids include sulphuric acid, sulphamic acid,phenolsulphonic acid, methane sulphonic acid and toluenesulphonic acid.

The acid or acids are present in a total concentration of 25-500 g/l ofthe composition (with respect to the composition), more preferably30-250 g/l, even more preferably 30-100 g/l.

The tin source is preferably present in the composition at aconcentration of 5-100 g/l (more preferably 15 to 60 g/l) with respectto the composition. Where a tin salt is the tin source it does not haveto be a salt of the mono-substituted benzenesulphonic acid or inorganicacid. Thus the composition may contain ions other than tin, sulphonateand those from the inorganic acid. Where the tin source is solid tin, itmay be as a tin anode which gradually dissolves as electrolysis proceedsto maintain a substantially constant concentration of tin ions in anelectroplating bath. Where the tin source is a tin salt it may bemetered to the electroplating bath so that as tin is electro-depositedfrom the bath, tin salt is added to the bath to maintain theconcentration of tin ions in the bath at a constant level.

An antioxidant may optionally be added. These materials retard theoxidation of divalent tin to tetravalent tin which may lead to sludgeformation and stannous tin loss. The preferred amount of antioxidant tobe added is in the range 1 to 50 g/l of the composition and mostpreferably from 2.5 to 20 g/l of the composition. Typical antioxidantshave been described for example in U.S. Pat. No. 3,749,649 and include1,2,3-trihydroxybenzene, 1,2-dihydroxybenzene,1,2-dihydroxybenzene-4-sulphonic acid,1,2-dihydroxybenzene-3,5-disulphonic acid, 1,4-dihydroxybenzene,1,4-dihydroxybenzene-2-sulphonic acid,1,4-dihydroxybenzene-2,5-disulphonic acid or vanadium pentoxide.

The composition of the present invention also comprises one or moreaddition agents containing a mono-, di- or tri-substituted phenol (eachoptionally alkoxylated) in which at least one of the substituentsincludes a secondary, tertiary or quaternary nitrogen atom. The phenolsare preferably 2,4 or 2,6-disubstituted or 2,4,6-trisubstituted phenols.

Addition agents have the general formula:

in which:

Y=alkylene, CH₂CH₂O or CH(CH₃)CH₂O

n³=0-10

n³=1 when Y=alkylene

R=a group of formula

in which:

R³=H, alkyl, aryl, hydroxyl or CHO, with the proviso that when R³ ishydroxyl or CHO, n²=1-3, and when R³ is H, alkyl or aryl, n² is 1,

R⁴=H, alkyl, cycloalkyl, hydroxyalkyl or alkoxyalkyl

R⁵=alkyl, optionally interrupted by O or N atoms, which may be furthersubstituted,

X=a phenol (optionally alkoxylated) radical, optionally furthersubstituted

n=0 or 1

n¹=1 to 7

when n=0, n¹=1

when n=1, n¹=1-7

R may optionally be the quaternary ammonium salt formed by reaction withacids such as, sulphuric acid, toluenesulphonic acid, sulphamic acid,phenolsulphonic acid and methanesulphonic acid.

R₁ and R₂ (which may be the same or different)=R, H or optionallysubstituted alkyl.

Especially preferable examples include:

As will be known to those skilled in the art such additives canconveniently be made by condensation of the phenol with an aldehyde andan amine under acidic or basic conditions. The molar proportions ofphenol to amine to aldehyde may be varied over a wide range typicallythe range will be from 1:1:1 to 1:2:2. As will be obvious to thoseskilled in the art such a reaction will give rise to a mixture ofmonomeric and polymeric products. The reaction products may also bealkoxylated with either ethylene or propylene oxide. Although anyphenol, amine and aldehyde may be used preferred examples include:

Phenols: ortho and/or para alkyl-phenols, where the alkyl group ismethyl, ethyl, isopropyl, n-butyl, sec-butyl, tert-butyl, isoamyl,hexyl, and nonyl; Diphenols: 2,2-bis(4-hydroxyphenyl)propane or4,4′-dihydroxydiphenylsulphone.

Aldehydes: formaldehyde, acetaldehyde, glyoxal.

Amines: methylamine, dimethylamine, ethylamine, diethylamine, n- oriso-propylamine, n- or sec-butylamine, n-hexylamine, ethanolamine,diethanolamine, n or iso-propanolamine, 2-aminobutanol, 4-aminobutanol,2-amino-5-diethylaminopentane, 2-(2-aminoethoxy)ethanol,2-(2-aminoethylamino)ethanol, 2-amino-2-ethyl-1,3-propandiol.

The compositions of the present invention when used for tin platingprovides a wider plating range and brighter plates with less surfacedefects than can be obtained by using other addition agents.

The surfaces which can be tin-plated using the compositions and methodsof the invention are those surfaces which may normally be tin-platede.g. steel or copper. The plated surfaces include those of strips andwires and the applicable processes include those involving the platingof strips and wires.

EXAMPLES Example 1

This example illustrates how the preferred addition agents may besynthesised using base catalysis.

Substituted phenol (1 mole), water (equivalent weight based on phenol)and sodium hydroxide (0.2 mole) were charged to the reactor. The mixturewas heated at 60° C. with agitation until a clear solution was obtained.

Amine (2 moles) was charged into a second reactor and aldehyde (2 moles)slowly added with stirring whilst keeping the temperature below 60° C.This solution was added to the alkylphenol solution in this firstreactor and the mixture heated at 100° C. for half an hour.

The following examples are illustrative of this method of synthesis.

TABLE 1 Example Number Phenol Amine Aldehyde 2 4-MethylphenolEthanolamine Formaldehyde 3 4-tert Butylphenol 2-(2-aminoethylamino)Formaldehyde ethanol 4 4,4′-Isopropylidene- Diethanolamine Formaldehydediphenol 5 4-Ethylphenol iso-Propanolamine Formaldehyde 6 4-tertButylphenol Diethanolamine Formaldehyde 7 4-tert ButylphenolEthanolamine Formaldehyde 8 3-Methylphenol Ethanolamine Glyoxal 94-nonylphenol 7 Ethanolamine Formaldehyde mole ethoxylate 10  4-tertButylphenol 2-amino-2-ethyl- Formaldehyde 1 mole ethoxylate propane-diol

Example 11

This example illustrates how the preferred addition agents may be madeusing acid catalysis.

Formaldehyde (2 moles) was slowly added to ethanolamine (2 moles) withstirring, the temperature being kept to below 60° C. Water (108 g) wasadded and the mixture acidified to pH 3 using sulphuric acid. Themixture was heated to 60° C. and p-cresol (1 mole) added, on completionof the addition the mixture was heated to 100° C. for 30 mins and thencooled.

The electroplating characteristics of various compositions weredetermined in a Hull Cell at 3 amps total current for 1 minute at 50° C.A 10 cm×6 cm steel plate, pre-cleaned by immersion in sodium hydroxidefollowed by a water rinse and immersion in 18.5% hydrochloric acid, wasused in all the following examples.

The aqueous compositions used are out in Table 2, Examples 12-22 areaccording to the invention whilst Examples 23 and 24 are provided forcomparison.

In examples 12 and 14 to 21 the composition included 1 g/l ofantioxidant (1,2-dihydroxybenzene-4-sulphonic acid). The tin source inall cases was tin sulphate in an amount of 30 g/l calculated as Sn⁺⁺.

TABLE 2 Addition Addition Agent Agent Plating Example Acid conc. (as perconc. Range No. Acid (g/l) example) (g/l) (A/dm²) × 10 12 Sulphuric 60(4) 6  15-67 13 PSA 60 (5) 6 5.4-90 14 PTSA/Sulphamic 10/50 9 parts(2) + 6 6.5-90 1 part (3) 15 PTSA/Sulphuric 40/50 (11) 6 5.4-37 16Benzenesulphonic 60 1 part (2) + 6  10-55 1 part (6) 17 Sulphuric 50 (8)6  11-82 18 Methanesulphonic 60 (7) 6 5.4-38 19 Methanesulphonic 50 (9)3   6-58 20 PTSA/Sulphuric 10/40 8 parts (3) + 5 5.4-70 2 parts (9) 21PTSA/Sulphuric 10/50 9 parts (2) + 6 5.4-90 1 part (9) 22 PSA 40 (10) 6 11-74 23 PSA 60 ENSA 6 4   9-54 24 PSA 60 Diphane V 6   7-52

All concentrations are in g/l of the composition including the water.

PSA is phenol sulphonic acid.

PTSA is para toluene sulphonic acid.

What is claimed is:
 1. A composition suitable for use in a process forelectroplating surfaces with tin, comprising a) one or more acidsselected from the group consisting of sulphuric acid, sulphamic acid,phenol-4-sulphonic acid; toluene-2 sulphonic acid, toluene4-sulphonicacid, and methane sulphonic acid; b) one or more addition agentsselected from the group consisting of a 2,4-di-substituted phenol, a2,6-di-substituted phenol, and a 2,4,6-tri-substituted phenol and thealkyolated forms thereof in which at least one of the substituentsincludes a secondary, tertiary or quaternary nitrogen atom, c) a tinsource and d) water.
 2. A composition as claimed in claim 1, wherein thetin source is a tin salt.
 3. A composition as claimed in claim 1,wherein the acid or acids are present in a total concentration of 25-500g/l of the composition.
 4. A composition as claimed in claim 3, whereinthe acid or acids are present in a concentration of 30-250 g/l.
 5. Acomposition as claimed in claim 4, wherein the acid or acids are presentin a concentration of 30-100 g/l.
 6. A composition as claimed in claim1, wherein the tin source is present in the composition at aconcentration of 5-100 g/l, with respect to the composition.
 7. Acomposition as claimed in claim 6, wherein the tin source is present inan amount of 15 to 60 g/l.
 8. A composition as claimed in any one of thepreceding claims, which also comprises an antioxidant.
 9. A compositionas claimed in claim 8, wherein the antioxidant is present in an amountof 1 to 50 g/l of the composition.
 10. A composition as claimed in claim9, wherein the antioxidant is present in an amount of from 2.5 to 20 g/lof the composition.
 11. A composition suitable for use in a process forelectroplating surfaces with tin, comprising a) one or more acidsselected from the group consisting of sulphuric acid, sulphamic acid,aryl sulphonic acids, alkyl sulphonic acids and alkanol sulphonic acids,b) one or more addition agents, c) a tin source and d) water, whereinthe one or more addition agent is selected from compounds of the generalformula:

in which: R¹ and R²=R, H, alkyl or substituted alkyl and may be the sameor different, Y=alkylene, CH₂CH₂O or CH(CH₃)CH₂O n³=0-10 n³=1 whenY=alkylene R=a group of formula:

in which: R³=H, alkyl, aryl, hydroxyl or CHO, with the proviso that whenR³ is hydroxyl or CHO, n²=1-3, and when R³ is H, alkyl or aryl, n² is 1,R⁴=H, alkyl, cycloalkyl, hydroxyalkyl or alkoxyalkyl, R⁵=alkyl,optionally interrupted by O or N atoms, which may be furthersubstituted, X=a phenol or an alkoxylated phenol radical, optionallyfurther substituted, n=0 or 1 n¹=1 to 7 when n=0, n¹=1 when n=1, n¹=1-7,or R is in the form of its a quaternary ammonium salt formed by reactionwith sulphuric acid, toluenesulphonic acid, sulphamic acid,phenolsulphonic acid or methanesulphonic acid.
 12. A method of tinplating a surface which comprises using a composition as claimed inclaim 1 or
 11. 13. A method as claimed in claim 12, wherein saidproccess is a strip or wire plating process.
 14. A composition asclaimed in claim 11, wherein the one or more addition agent is selectedfrom the group consisting of formula (a), formula (b), formula (c) andformula (d) as defined below:

wherein R₁ is CH₃, CH₂CH₃, CH(CH₃)₂ or C(CH₃)₃; n=1-7; and x=0-10;

wherein R₁=CH₃CH₂CH₃, CH(CH₃)₂ or C(CH₃)₃;

wherein R₁ is CH₃, CH₂CH₃, CH(CH₃)₂ or C(CH₃)₃ and n=1-7; and

wherein R is —CH₂NHCH₂CH₂NHCH₂CH₂OH; R¹ is CH₃, CH₂CH₃ or C(CH₃)₃ and R²is H or is R.